Some high power tetrodes are not suitable for grounded grid and they are damaged by trying to operate them in that manner, maybe that is what your friend is thinking about. But they won't put out power in any configuration once damaged by grounded grid operation.
4-1000 tubes are well suited to grounded grid but if the tube is still operational it will also operate just find\e in traditional grounded cathode, grid fed operation.
Now of course once a tube has been used for SSB it will never be able to produce a proper carrier again